1. Field of the Invention
The invention relates to drilling processes for recovering methane from coal mine gob areas through degas holes.
2. Prior Art
The hazards associated with methane presence in a breathable air atmosphere in coal mines are well known. Such methane is generally accepted as being either in the coal itself or surrounding strata. Such surrounding strata containing methane can be above or below the coal seam and may or may not communicate with the mine through cracks or fractures, either naturally occurring or as are created in a mining process.
Until recent years methane presence has been viewed solely as a hazard and has been removed at the coal seam face or through horizontal holes drilled into the seam face for venting. Recently, vertical degas holes drilled from the surface to the seam or just above it have been utilized to degas coal mines, with the collected gas being vented or saved and transported for commercial use. Where longwall mining is practiced, such vertical wells are placed above the seam to be minded. As mining advances the ceiling is controlled and allowed to fall in as the roof supports are advanced. The vertical hole is placed to draw from both the methane released from the coal seam being mined and the adjacent strata that caves or fractures into the extracted mine panel. Experience has suggested that such vertical holes be no closer than the width at the seam end and near the center line but may be offset to maintain integrity. The practicality and feasibility of this drilling is, of course, dependent upon the ground conditions above the coal seam and the seam depth.
The present invention, like an earlier patent application of one of the present inventors, in a "Coal Gasification Well Drilling Process", U.S. Ser.No. 179,663 now U.S. Pat. No. 4,858,689, employs directional drilling techniques. With the present process, such directional drilling techniques are employed to drill one or more degas holes to curve so as to be parallel, near parallel or slanted and spaced an optimum distance above a coal seam to be subjected to the effects of longwall or retreat mining. Directional drilling of injection and production well bores for coal gasification processes are shown in the Collins U.S. Pat. Nos. No. 4,422,505, and the Garkusha, et al. U.S. Pat. No. 4,573,531. The arrangement, purpose and operation of the processes disclosed in these patents are accordingly unlike the present invention. Similarly distinct from the present invention, the Zakiewicz U.S. Pat. No. 4,249,775, is directed to a method for mining sulphur.
The present invention, unlike such earlier minerals and hydrocarbon recovery systems, utilizes directional drilling techniques for forming one or more degas holes located in advance of mining above and to curve to be essentially parallel, near parallel or slanted and spaced a certain distance above a coal seam to be mined. Similarly, a directionally drilled degas borehole may be drilled subsequent to mining above abandoned mine workings to recover methane gas. The formed hole is for recovery of methane gas from the seam front and the adjacent rock strata that is in communication with the gob area of the coal mine.